I found these tutorials on http://moodle.robotics101.com/index.php. It's very good for begginers who don't know much about electronics. Although they are for a pic, a lot of the concepts are the same as avr. Normally you have to make an account to get them, and although it's free it's annoying so I got the pdfs for you. They're attached at the bottom of the page. Also at times the author makes references to later chapters which he hasn't put out yet or plans to put out considering he hasn't touched the site in forever. I have a similair post on the software page about programming. http://www.societyofrobots.com/robotforum/index.php?topic=6765.0